That night Tom and Huck take the dead cat to the graveyard, where there they hear voices belonging to Muff Potter (the town drunk), Dr. Robinson, and Injun Joe. Dr. Robinson has paid Muff Potter and Injun Joe to dig up the corpse for his medical research. After a fight between the three men, in which Muff Potter is knocked unconscious, Injun Joe stabs Dr. Robinson with Muff's knife. Huck and Tom flee and do not hear Injun Joe convince the drunken Muff that he is the murderer.
Tom and Huck run to the old tannery, where they discuss the dilemma they're in. They both realize that if they reveal Injun Joe as the murderer, he will kill them. The boys take an oath to not reveal what they have seen. Suddenly, they hear a stray dog barking. Thinking it is an evil omen, both boys temporarily renounce their wicked ways.
By noon the next day, the entire town of St. Petersburg knows about Dr. Robinson's murder, and they know that the murder weapon was Muff Potter's knife. School is dismissed for the afternoon, and everyone gravitates to the graveyard, where the sheriff is with Muff Potter, who initially proclaims his innocence. But finally, in despair, Muff tells Injun Joe to reveal the truth. Injun Joe, of course, makes sure that all of the guilt is placed on Muff Potter.
Listening to Injun Joe's lies and machinations, the two boys begin to feel conscience-stricken about their silence. Tom's conscience bothers him so much that he eases it by "smuggling small comforts" to the prisoner, but he can't escape his conscience altogether. At night, he is troubled by wild dreams, and he often talks in his sleep about blood and murder and graves, but his mumblings make no sense.
Superstitions pervade these chapters and mark a new direction that the novel will take. First, superstition is seen in the many sounds that Tom hears and in the various signs that Tom and Huck encounter. At the graveyard, the boys discuss the powers of dead people; they believe that spirits of the dead can hear people talking and can see them in the dark. This discussion leads to the various superstitions connected with the entire Injun Joe episode.
Until this point in the novel, Twain has shown the childhood adventures of Tom and some of his friends to be all innocent fun. That is, Tom is the mischievous boy playing various types of pranks, creating great adventures using pirates and robbers, and fighting great wars. Furthermore, Tom has been seen in terms of his relationships at home, at school, at Sunday school, and at play with his friends. In this chapter, there begins a simple adventure in the graveyard concerning a dead cat. This adventure, however, is vastly different from anything that Tom or Huck have previously confronted. In the person of Injun Joe, Tom and Huck have their first encounter with pure evil. They witness first a grave robbery, then an argument, and finally a fight that ends in a murder.
Two new characters are also introduced in this chapter: Muff Potter and Injun Joe. Muff Potter is the town's disgrace--a drunk and worthless person who is hired to help dig up the corpse of the recently buried Hoss Williams. Muff is not very bright and is easily persuaded by Injun Joe that he is the murderer. Muff's trust in Injun Joe indicates his simple-mindedness. After the murder, Potter is depicted as fearful, weak, hopeless, confused, and literally shaking, partly from alcohol and partly from fear. The townspeople take advantage of his weakness and willingly believe Injun Joe; they condemn Muff Potter on the basis of rumor and hearsay even before any formal accusation is made against him.
In contrast, Injun Joe is a vicious, wicked, and evil man. The murder of Dr. Robinson is not the first murder that he has committed, and he later has no compunction about mutilating Widow Douglas. He is the personification of evil, and his evil is seen in his willingness to kill a man for revenge or for some trivial reason. The townspeople are willing to believe Injun Joe because they are afraid of him and fear retaliation from him. Thus Huck and Tom are right in their fear of Injun Joe. Future chapters show Tom and Huck helping Old Muff Potter and being deeply frightened by Injun Joe.
Twain's literary artistry is seen in the techniques he uses to depict Injun Joe. He never comments directly on Injun Joe's evil. Instead, he shows how evil Injun Joe is by the boys' reaction to him. Here are two boys in the cemetery at midnight: Thoughts of dead people don't scare them. Thoughts of ghosts don't scare them. Even thoughts of the devil don't scare them. But they are pushed to panic by the presence of Injun Joe. Their reaction to his presence is more effective than a straightforward statement of his evil would be.
In this chapter, the two boys flee from the murder scene, "speechless with horror." They are confronted with real evil and with the realization that if they tell, their lives will be in jeopardy. This situation contrasts dramatically with their make-believe adventures in which death is an exciting--and imaginary--prospect. To protect themselves, the boys agree to remain silent, and they make a complicated ritual of this oath-taking, a ritual that involves both writing out the oath and signing it in blood--a technique that Tom has learned from the books he has read. Taking this blood vow later makes Tom reluctant to reveal the truth.
In these chapters, Tom's world has suddenly reversed itself. The days of happy childhood pleasures and adventures are gone: Aunt Polly does not scold him as usual; instead she weeps over him, which is much more upsetting. At school, Tom is flogged for playing hooky the preceding afternoon, but he hardly notices the punishment because his mind is occupied with the horrors of the preceding night. And, when Becky returns his brass doorknob, his world of childhood innocence is temporarily brought to an end.
"All the old graves were sunken in." A reference to the fact that a mound over the grave meant that a new coffin has just been buried and the displaced soil mounded up over the coffin.
lugubrious very sad or mournful, especially in a way that seems exaggerated or ridiculous.